Light detecting element

ABSTRACT

This light detecting element has a simple configuration, and is highly sensitive to a prescribed wavelength region. The light detecting element comprises a positive electrode, a negative electrode, and an active layer that is provided between the positive electrode and the negative electrode, and that includes a p-type semiconductor material and n-type semiconductor material. The thickness of the active layer is at least 800 nm. The weight ratio between the p-type semiconductor material and the n-type semiconductor material included in the active layer (p/n ratio) is at most 99/1. The work function of the negative electrode side surface in contact with the active layer is lower than the absolute value of the LUMO energy level of the n-type semiconductor material.

TECHNICAL FIELD

The present invention relates to a photoelectric conversion element, particularly a light detecting element.

BACKGROUND ART

The photoelectric conversion element has been attracting attention as a very useful device from the viewpoint of energy saving and reduction of carbon dioxide emissions, for example.

The photoelectric conversion element includes at least a pair of electrodes including a positive electrode and a negative electrode, and an active layer provided between the pair of electrodes. In the photoelectric conversion element, one of the electrodes is made of a transparent or translucent material, and light is incident on the active layer from the transparent or translucent electrode side. The energy (hυ) of light incident on the active layer generates electric charges (holes and electrons) in the active layer, the generated holes move toward the positive electrode, and the electrons move toward the negative electrode. Then, the electric charges that have reached the positive electrode and the negative electrode are taken out of the photoelectric conversion element via the electrodes.

Among the photoelectric conversion elements, particularly, a light detecting element has been used in an image sensor, various biometric authentication devices, and the like, and requires sensitivity in a detection wavelength region, that is, a predetermined wavelength region depending on the application, and thus various studies have been conducted in recent years.

In the related art, commonly used light detecting elements usually have sensitivity in a wide region from a visible light region to a near infrared region, and for example, in order to further increase the sensitivity in a predetermined detection wavelength region such as the near infrared wavelength region, an optical member such as an optical filter that selectively blocks light having a wavelength outside the detection wavelength region has been used (refer to Patent Document 1).

PRIOR ART DOCUMENTS Non-Patent Document

-   Patent Document 1: JP-A-2014-22675

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the light detecting element according to Patent Document 1, since additional components such as an optical member for realizing a desired function are indispensable, not only the structure becomes complicated but also high sensitivity in a desired detection wavelength region cannot be obtained in some cases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a light detecting element capable of improving sensitivity in a predetermined detection wavelength region with a simpler configuration.

Means for Solving the Problems

As a result of diligent studies to solve the above problems, the present inventors have found that the above problems can be solved if the following requirements are satisfied, and have completed the present invention. That is, the present invention provides the following [1] to [8].

[1] A light detecting element including a positive electrode, a negative electrode, and an active layer provided between the positive electrode and the negative electrode and containing a p-type semiconductor material and an n-type semiconductor material,

wherein a thickness of the active layer is at least 800 nm,

a weight ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material contained in the active layer is at most 99/1, and

a work function of a surface in contact with the active layer on the negative electrode side is lower than an absolute value of a LUMO energy level of the n-type semiconductor material.

[2] The light detecting element according to [1], wherein external quantum efficiency has a narrow peak in a near infrared wavelength region.

[3] The light detecting element according to [2], wherein a full width at half maximum of the narrow peak is at most less than 300 nm.

[4] The light detecting element according to any one of [1] to [3], wherein the surface is a surface of an electron transport layer provided between the negative electrode and the active layer.

[5] The light detecting element according to any one of [1] to [4], wherein the n-type semiconductor material is a fullerene derivative.

[6] The light detecting element according to [5], wherein the fullerene derivative is C70PCBM.

[7] The light detecting element according to any one of [2] to [6], wherein in a visible light wavelength region, the external quantum efficiency at the maximum absorption wavelength of the active layer is at most 20% of the maximum value of the external quantum efficiency of the narrow peak.

[8] An image sensor including the light detecting element according to any one of [1] to [7].

Effect of the Invention

According to the present invention, it is possible to provide a light detecting element having high sensitivity in a predetermined wavelength region with a simpler configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a photoelectric conversion element (light detecting element).

FIG. 2 is a diagram schematically illustrating a configuration example of an image detector.

FIG. 3 is a diagram schematically illustrating a configuration example of a fingerprint detector.

FIG. 4 is a graph illustrating an EQE spectrum of a light detecting element and an absorption spectrum of an active layer.

FIG. 5 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 6 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 7 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 8 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 9 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 10 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 11 is a graph illustrating the EQE spectrum of the light detecting element and the absorption spectrum of the active layer.

FIG. 12 is a graph illustrating the EQE spectrum of the light detecting element.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a photoelectric conversion element according to an embodiment of the present invention will be described with reference to the drawings. Note that the drawings merely outline the shapes, sizes, and arrangements of components to the extent that the invention can be understood. The present invention is not limited to the following description, and each component can be appropriately modified without departing from the gist of the present invention. Further, in the configuration according to the embodiment of the present invention, it is not always produced or used in the arrangement illustrated in the drawings. In each of the drawings described below, the same components may be given the same sign and the description thereof may be omitted.

Here, first, terms commonly used in the following description will be described.

The “polymer compound” means a polymer having a molecular weight distribution and having a polystyrene-equivalent number average molecular weight of 1×10³ or more and 1×10⁸ or less. Constituent units contained in the polymer compound are 100 mol % in total.

The “constituent unit” means a unit existing in one or more in a polymer compound.

A “hydrogen atom” may be a light hydrogen atom or a deuterium atom.

A “halogen atom” includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The meaning of “may have a substituent” includes a case where all the hydrogen atoms constituting the compound or group are unsubstituted, and a case where some or all of one or more hydrogen atoms are substituted by the substituent.

Unless otherwise specified, the “alkyl group” may be linear, branched, or cyclic. The number of carbon atoms of the linear alkyl group is usually 1 to 50, preferably 1 to 30, and more preferably 1 to 20 without including the number of carbon atoms of the substituent. The number of carbon atoms of a branched or cyclic alkyl group is usually 3 to 50, preferably 3 to 30, and more preferably 4 to 20 without including the number of carbon atoms of the substituent.

The alkyl group may have a substituent. Specific examples of the alkyl group include an alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isoamyl group, a 2-ethylbutyl group, an n-hexyl group, a cyclohexyl group, an n-heptyl group, a cyclohexylmethyl group, a cyclohexylethyl group, an n-octyl group, a 2-ethylhexyl group, a 3-n-propylheptyl group, an adamantyl group, an n-decyl group, a 3,7-dimethyloctyl group, a 2-ethyloctyl group, a 2-n-hexyl-decyl group, an n-dodecyl group, a tetradecyl group, a hexadecyl group, an octadecyl group, and an eicosyl group; and an alkyl group having a substituent such as a trifluoromethyl group, a pentafluoroethyl group, a perfluorobutyl group, a perfluorohexyl group, a perfluorooctyl group, a 3-phenylpropyl group, a 3-(4-methylphenyl) propyl group, a 3-(3,5-di-n-hexylphenyl) propyl group, and a 6-ethyloxyhexyl group.

An “aryl group” means a remaining atomic group obtained by removing one hydrogen atom directly bonded to a carbon atom constituting a ring from an aromatic hydrocarbon which may have a substituent.

The aryl group may have a substituent. Specific examples of the aryl group include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 1-anthrasenyl group, a 2-anthrasenyl group, a 9-anthrasenyl group, a 1-pyrenyl group, a 2-pyrenyl group, a 4-pyrenyl group, a 2-fluorenyl group, a 3-fluorenyl group, a 4-fluorenyl group, a 2-phenylphenyl group, a 3-phenylphenyl group, a 4-phenylphenyl group, and a group having a substituent such as an alkyl group, an alkoxy group, an aryl group, and a fluorine atom.

An “alkoxy group” may be linear, branched, or cyclic. The number of carbon atoms of the linear alkoxy group is usually 1 to 40 and preferably 1 to 10 without including the number of carbon atoms of the substituent. The number of carbon atoms of the branched or cyclic alkoxy group is usually 3 to 40 and preferably 4 to 10 without including the number of carbon atoms of the substituent.

The alkoxy group may have a substituent. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a tert-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, a cyclohexyloxy group, an n-heptyloxy group, an n-octyloxy group, a 2-ethylhexyloxy group, an n-nonyloxy group, an n-decyloxy group, a 3,7-dimethyloctyloxy group, and a lauryloxy group.

The number of carbon atoms of the “aryloxy group” is usually 6 to 60 and preferably 6 to 48 without including the number of carbon atoms of the substituent.

The aryloxy group may have a substituent. Specific examples of the aryloxy group include a phenoxy group, a 1-naphthyloxy group, a 2-naphthyloxy group, a 1-anthrasenyloxy group, a 9-anthrasenyloxy group, a 1-pyrenyloxy group, and a group having a substituent such as an alkyl group, an alkoxy group, and a fluorine atom.

An “alkylthio group” may be linear, branched, or cyclic. The number of carbon atoms of the linear alkylthio group is usually 1 to 40 and preferably 1 to 10 without including the number of carbon atoms of the substituent. The number of carbon atoms of the branched and cyclic alkylthio groups is usually 3 to 40 and preferably 4 to 10 without including the number of carbon atoms of the substituent.

The alkylthio group may have a substituent. Specific examples of the alkylthio group include a methylthio group, an ethylthio group, a propylthio group, an isopropylthio group, a butylthio group, an isobutylthio group, a tert-butylthio group, a pentylthio group, a hexylthio group, a cyclohexylthio group, a heptylthio group, an octylthio group, a 2-ethylhexylthio group, a nonylthio group, a decylthio group, a 3,7-dimethyloctylthio group, a laurylthio group, and a trifluoromethylthio group.

The number of carbon atoms of an “arylthio group” is usually 6 to 60 and preferably 6 to 48 without including the number of carbon atoms of the substituent.

The arylthio group may have a substituent. Examples of the arylthio group include a phenylthio group and a C1 to C12 alkyloxyphenylthio group (here, “C1 to C12” indicates that the group to be described immediately after that has 1 to 12 carbon atoms. The same applies to the following), a C1 to C12 alkylphenylthio group, a 1-naphthylthio group, a 2-naphthylthio group, and a pentafluorophenylthio group.

A “p-valent heterocyclic group” (p represents an integer of 1 or more) means a remaining atomic group excluding p hydrogen atoms among the hydrogen atoms directly bonded to a carbon atom or a hetero atom constituting a ring from a heterocyclic compound that may have a substituent. Among the p-valent heterocyclic groups, a “p-valent aromatic heterocyclic group” is preferable. The “p-valent aromatic heterocyclic group” means a remaining atomic group excluding p hydrogen atoms among the hydrogen atoms directly bonded to a carbon atom or a hetero atom constituting a ring from an aromatic heterocyclic compound that may have a substituent.

Examples of the substituent that the heterocyclic compound may have include a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a monovalent heterocyclic group, a substituted amino group, an acyl group, an imine residue, an amide group, an acidimide group, a substituted oxycarbonyl group, an alkenyl group, an alkynyl group, a cyano group, and a nitro group.

Examples of the aromatic heterocyclic compound include a compound in which an aromatic ring is fused to the heterocycle even if the heterocycle itself does not exhibit aromaticity in addition to the compound in which the heterocycle itself exhibits aromaticity.

Among the aromatic heterocyclic compounds, specific examples of the compound in which the heterocycle itself exhibits aromaticity include oxadiazole, thiadiazole, thiazole, oxazol, thiophene, pyrrole, phosphole, furan, pyridine, pyrazine, pyrimidine, triazine, pyridazine, quinoline, isoquinolin, carbazole, and dibenzophosphol.

Among the aromatic heterocyclic compounds, specific examples of compounds in which the aromatic heterocycle itself does not exhibit aromaticity and the aromatic ring is fused to the heterocycle include phenoxazine, phenothiazine, dibenzoborol, dibenzosiror, and benzopyran.

The number of carbon atoms of the monovalent heterocyclic group is usually 2 to 60 and preferably 4 to 20 without including the number of carbon atoms of the substituent.

The monovalent heterocyclic group may have a substituent, and specific examples of the monovalent heterocyclic group include a thienyl group, a pyrrolyl group, a furyl group, a pyridyl group, a piperidyl group, a quinolyl group, an isoquinolyl group, a pyrimidinyl group, a triazinyl group, and a group having a substituent such as an alkyl group and an alkoxy group.

The “substituted amino group” means an amino group having a substituent. Examples of substituents that an amino group has include an alkyl group, an aryl group, and a monovalent heterocyclic group. As the substituent, an alkyl group, an aryl group, or a monovalent heterocyclic group is preferable. The number of carbon atoms of the substituted amino group is usually 2 to 30.

Examples of the substituted amino group include a dialkylamino group such as a dimethylamino group and a diethylamino group, a diarylamino group such as a diphenylamino group, a bis(4-methylphenyl) amino group, a bis(4-tert-butylphenyl) amino group, and a bis(3,5-di-tert-butylphenyl) amino group.

The “acyl group” usually has about 2 to 20 carbon atoms, and preferably 2 to 18 carbon atoms. Specific examples of the acyl group include an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a pivaloyl group, a benzoyl group, a trifluoroacetyl group, and a pentafluorobenzoyl group.

The “imine residue” means a remaining atomic group obtained by removing one hydrogen atom directly bonded to a carbon atom or a nitrogen atom forming a carbon atom-nitrogen atom double bond from an imine compound. The “imine compound” means an organic compound having a carbon atom-nitrogen atom double bond in a molecule. Examples of the imine compound include aldimine, ketimine, and a compound in which the hydrogen atom bonded to the nitrogen atom constituting the carbon atom-nitrogen atom double bond in aldimine is replaced with an alkyl group or the like.

The imine residue usually has about 2 to 20 carbon atoms, and preferably 2 to 18 carbon atoms. Examples of the imine residue include groups represented by the following structural formulas.

The “amide group” means a remaining atomic group obtained by removing one hydrogen atom bonded to a nitrogen atom from the amide. The number of carbon atoms of the amide group is usually about 1 to 20 and preferably 1 to 18. Specific examples of the amide group include a formamide group, an acetamido group, a propioamide group, a butyroamide group, a benzamide group, a trifluoroacetamide group, a pentafluorobenzamide group, a diformamide group, a diacetamide group, a dipropioamide group, a dibutyroamide group, a dibenzamide group, a ditrifluoroacetamide group, and a dipentafluorobenzamide group.

The “acidimide group” means a remaining atomic group obtained by removing one hydrogen atom bonded to a nitrogen atom from the acidimide. The number of carbon atoms of the acidimide group is usually about 4 to 20. Specific examples of the acidimide group include a group represented by the following structural formulas.

The “substituted oxycarbonyl group” means a group represented by R′—O—(C═O)—.

Here, R′ represents an alkyl group, an aryl group, an arylalkyl group, or a monovalent heterocyclic group.

The substituted oxycarbonyl group usually has about 2 to 60 carbon atoms and preferably 2 to 48 carbon atoms.

Specific examples of the substituted oxycarbonyl group include a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, an isopropoxycarbonyl group, a butoxycarbonyl group, an isobutoxycarbonyl group, a tert-butoxycarbonyl group, a pentyloxycarbonyl group, a hexyloxycarbonyl group, a cyclohexyloxycarbonyl group, a heptyloxycarbonyl group, an octyloxycarbonyl group, a 2-ethylhexyloxycarbonyl group, a nonyloxycarbonyl group, a decyloxycarbonyl group, a 3,7-dimethyloctyloxycarbonyl group, a dodecyloxycarbonyl group, a trifluoromethoxycarbonyl group, a pentafluoroethoxycarbonyl group, a perfluorobutoxycarbonyl group, a perfluorohexyloxycarbonyl group, a perfluorooctyloxycarbonyl group, a phenoxycarbonyl group, a naphthoxycarbonyl group, and a pyridyloxycarbonyl group.

The “alkenyl group” may be linear, branched, or cyclic. The number of carbon atoms of the linear alkenyl group is usually 2 to 30 and preferably 3 to 20 without including the number of carbon atoms of the substituent. The number of carbon atoms of the branched or cyclic alkenyl group is usually 3 to 30 and preferably 4 to 20 without including the number of carbon atoms of the substituent.

The alkenyl group may have a substituent. Specific examples of the alkenyl group include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 2-butenyl group, a 3-butenyl group, a 3-pentenyl group, a 4-pentenyl group, a 1-hexenyl group, a 5-hexenyl group, a 7-octenyl group, and a group having a substituent such as an alkyl group and an alkoxy group.

The “alkynyl group” may be linear, branched, or cyclic. The number of carbon atoms of the linear alkenyl group is usually 2 to 20 and preferably 3 to 20 without including the number of carbon atoms of the substituent. The number of carbon atoms of the branched or cyclic alkenyl group is usually 4 to 30 and preferably 4 to 20 without including the number of carbon atoms of the substituent.

The alkynyl group may have a substituent. Specific examples of the alkynyl group include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 3-pentynyl group, a 4-pentynyl group, a 1-hexynyl group, a 5-hexynyl group, and a group having a substituent such as an alkyl group and an alkoxy group.

[1. Light Detecting Element]

A light detecting element (photoelectric conversion element) according to the present embodiment includes a positive electrode, a negative electrode, and an active layer provided between the positive electrode and the negative electrode, and containing a p-type semiconductor material and an n-type semiconductor material, in which a thickness of the active layer is at least 800 nm, a weight ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material contained in the active layer is at most 99/1, and a work function of a surface in contact with the active layer on the negative electrode side is lower than an absolute value of a LUMO energy level of the n-type semiconductor material.

Here, “LUMO” (Lowest Unoccupied Molecular Orbital) means the lowest empty orbital.

The LUMO level of n-type semiconductor materials can be estimated from cyclic voltammetry (CV) measurement values. The CV measurement for evaluating the LUMO level can be performed, for example, according to the method described in Advanced Materials, Vol. 18, 2006, pp. 789-794.

With reference to FIG. 1, a configuration example of the light detecting element according to the present embodiment will be described. A configuration example of a light detecting element having a so-called reverse laminated structure will be described.

FIG. 1 is a diagram schematically illustrating a light detecting element according to an embodiment of the present invention.

As illustrated in FIG. 1, the light detecting element 10 of the present embodiment is provided on, for example, a support substrate 11. The light detecting element 10 includes a negative electrode 12 provided in contact with the support substrate 11, an electron transport layer 13 provided in contact with the negative electrode 12, an active layer 14 provided in contact with the electron transport layer 13, a hole transport layer 15 provided in contact with the active layer 14, and a positive electrode 16 provided in contact with the hole transport layer 15. In this configuration example, a sealing substrate 17 provided in contact with the negative electrode is further provided.

Hereinafter, the components that can be contained in the light detecting element of the present embodiment will be specifically described.

(Substrate)

The light detecting element is usually formed on a substrate (support substrate or sealing substrate). A pair of electrodes, usually formed of a negative electrode and a positive electrode, are formed on this substrate. A material of the substrate is not particularly limited as long as it is a material that does not chemically change when forming a layer containing, particularly, an organic compound.

Examples of the material of the substrate include glass, plastic, a polymer film, and silicon. In a case of an opaque substrate, it is preferable that an electrode (that is, the electrode on the side far from the opaque substrate) on the side opposite to the electrode provided on the opaque substrate side is a transparent or translucent electrode.

(Electrode)

The light detecting element includes a pair of electrodes, a positive electrode and a negative electrode. At least one of the positive electrode and the negative electrode is preferably a transparent or translucent electrode in order to allow light to enter.

Examples of the material of the transparent or translucent electrode include a conductive metal oxide film and a translucent metal thin film. Specific examples of the electrode material include conductive materials such as indium oxide, zinc oxide, tin oxide, and indium tin oxide (ITO), indium zinc oxide (IZO), and NESA, which are composites thereof, and gold, platinum, silver, and copper. As a transparent or translucent electrode material, ITO, IZO, and tin oxide are preferable. Further, as the electrode, a transparent conductive film using an organic compound such as polyaniline and a derivative thereof, or polythiophene and a derivative thereof as a material may be used. The transparent or translucent electrode may be a positive electrode or a negative electrode.

If one of the pair of electrodes is transparent or translucent, the other electrode may be an electrode having low light transmittance. Examples of the material of the electrode having low light transmittance include metal and a conductive polymer. Specific examples of material of the electrode having low light transmittance include metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, aluminum, scandium, vanadium, zinc, yttrium, indium, cerium, samarium, europium, terbium, and ytterbium, and alloys of two or more of these, or alloys of one or more of these metals with one or more metals selected from the group consisting of gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten, and tin, graphite, a graphite interlayer compound, polyaniline and a derivative thereof, and polythiophene and a derivative thereof. Examples of the alloys include a magnesium-silver alloy, a magnesium-indium alloy, a magnesium-aluminum alloy, an indium-silver alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, a lithium-indium alloy, and a calcium-aluminum alloy.

As a method for forming an electrode, any suitable forming method known in the related art can be used. Examples of the method for forming an electrode include a vacuum deposition method, a sputtering method, an ion plating method, and a plating method.

(Active Layer)

The active layer contains a p-type semiconductor material (electron-donating compound) and an n-type semiconductor material (electron-accepting compound) (details of suitable p-type semiconductor material and n-type semiconductor material will be described later). Whether it is the p-type semiconductor material or the n-type semiconductor material can be relatively determined from a HOMO energy level or a LUMO energy level of the selected compound.

In the present embodiment, the thickness of the active layer is at least 800 nm, preferably 800 nm or more and 10000 nm or less from the viewpoint of improving the sensitivity of the light detecting element in a predetermined wavelength region, particularly in the near infrared wavelength region (780 nm to 2500 nm), and it is more preferably 800 nm or more and 2000 nm or less from the viewpoint of producing an active layer having a uniform thickness.

By adjusting the thickness of the active layer within the above range, the sensitivity of the light detecting element outside the predetermined wavelength region, particularly outside the near infrared wavelength region having a wavelength of less than 780 nm can be specifically reduced, and the sensitivity of the light detecting element in a predetermined narrow wavelength region, particularly in the narrow wavelength region of the near infrared wavelength region can be more improved.

The active layer includes a p-type semiconductor material and an n-type semiconductor material.

In the light detecting element of the present embodiment, the external quantum efficiency at the maximum absorption wavelength of the active layer in the visible light wavelength region (wavelength 360 nm to 830 nm) is preferably at most 20% with respect to the maximum value of the external quantum efficiency of the narrow peak, particularly, from the viewpoint of improving the sensitivity in a predetermined wavelength region, it is preferably set to at most 10%.

Specifically, in order for the external quantum efficiency (EQE) to have a narrow peak in a predetermined wavelength region, for example, a near infrared wavelength region, a p-type semiconductor material and/or an n-type semiconductor material contained in the active layer are preferably selected so that the absorption peak of the active layer is located in the vicinity of the near infrared wavelength region. At this time, it is preferably selected so that the external quantum efficiency at the absorption peak wavelength on the near infrared wavelength region side (particularly in the vicinity of the near infrared wavelength region) in the visible light wavelength region of the p-type semiconductor material and/or the n-type semiconductor material is at most 20% when the maximum value of the external quantum efficiency in a narrow peak is 100%. In other words, the p-type semiconductor material and/or the n-type semiconductor material contained in the active layer is preferably selected so as to be at the external quantum efficiency, for example, it is preferable that the external quantum efficiency at the starting point (lowest hem edge) on the low wavelength side of the mountain-shaped narrow peak that occurs in the near infrared wavelength region is at most 20% when the maximum value of the external quantum efficiency at the narrow peak is 100%.

Here, the “external quantum efficiency (EQE)” specifically refers to a value indicating a number of electrons, by a ratio (%), which can be taken out of the light detecting element, among the electrons generated for the number of photons with which the light detecting element is irradiated.

Further, the “narrow peak” means, for example, a mountain-shaped peak of external quantum efficiency that occurs in the near infrared wavelength region and has a predetermined full width at half maximum, which will be described later.

The active layer can preferably be formed by a coating method. Details of the p-type semiconductor material and the n-type semiconductor material that can be contained in the active layer and the method for forming the active layer will be described later.

(Intermediate Layer)

As illustrated in FIG. 1, the light detecting element of the present embodiment preferably includes an intermediate layer such as a charge transport layer (electron transport layer, hole transport layer, electron injection layer, hole injection layer) as a component for improving the characteristics.

As the material used for such an intermediate layer, for example, any suitable material known in the related art that contributes to the transfer of electric charge in the layer constituting the light detecting element can be used. Examples of the material of the intermediate layer include halides of alkali metals or alkaline earth metals such as lithium fluoride, and oxides such as molybdenum oxide.

Examples of the materials used for the intermediate layer include fine particles of inorganic oxides (semiconductors) such as titanium oxide and zinc oxide, and a mixture (PEDOT:PSS) of PEDOT (poly(3,4-ethylenedioxythiophene)) and PSS (poly(4-(styrene sulfonate)).

As illustrated in FIG. 1, the light detecting element of the present embodiment may include an electron transport layer as the intermediate layer between the negative electrode and the active layer. The electron transport layer has a function of transporting electrons from the active layer to the negative electrode. The electron transport layer may be in contact with the negative electrode. The electron transport layer may be in contact with the active layer.

The electron transport layer provided in contact with the negative electrode may be particularly referred to as an electron injection layer. The electron transport layer (electron injection layer) provided in contact with the negative electrode has a function of promoting the injection of electrons generated in the active layer into the negative electrode.

The electron transport layer contains an electron transport material. Examples of the electron transport material include polyalkyleneimine and a derivative thereof, a polymer compound having a fluorene structure, and metal oxide.

The electron transport layer preferably contains polyalkyleneimine or a derivative thereof, or metal oxide.

Examples of polyalkyleneimine and a derivative thereof include alkyleneimine having 2 to 8 carbon atoms such as ethyleneimine, propyleneimine, butyleneimine, dimethylethyleneimine, pentyleneimine, hexyleneimine, heptyleneimine, and octyleneimine, particularly, polymers obtained by polymerizing one or two or more of alkyleneimines having 2 to 4 carbon atoms by a common method, and a polymers that are chemically modified by reacting them with various compounds. As the polyalkyleneimine and a derivative thereof, polyethyleneimine ethoxylate (PEIE: ethoxylated polyethyleneimine) containing polyethyleneimine (PEI) and polyalkyleneimine as a main chain, and ethylene oxide which is a modified product added to nitrogen atoms in the main chain is preferable.

Examples of the polymer compound having a fluorene structure include poly[(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene)-ortho-2,7-(9,9′-dioctylfluorene)] (PFN) and PFN-P2.

Examples of the metal oxide include zinc oxide, gallium-doped zinc oxide, aluminum-doped zinc oxide, titanium oxide, and niobium oxide. As the metal oxide, a metal oxide containing zinc is preferable, and zinc oxide is particularly preferable.

Examples of other electron transport materials include poly(4-vinylphenol) and perylene diimide.

In the light detecting element of the present invention, the work function of the surface in contact with the active layer on the negative electrode side is lower than the absolute value of the LUMO energy level of the n-type semiconductor material contained in the active layer. In other words, a difference between the work function of the surface in contact with the active layer on the negative electrode side and the absolute value of the LUMO energy level of the n-type semiconductor material contained in the active layer is set to be a negative value.

Here, specific examples of the surface in contact with the active layer on the negative electrode side include the surface of the negative electrode and the surface of the electron transport layer provided between the negative electrode and the active layer. For example, in a case where the intermediate layer such as the electron transport layer (electron injection layer) is not formed, the “surface in contact with the active layer on the negative electrode side” is the surface of the negative electrode, and in a case where the electron transport layer (electron injection layer) is used as the intermediate layer, the “surface in contact with the active layer on the negative electrode side” is the surface of the electron transport layer (electron injection layer).

The work function of the surface in contact with the active layer on the negative electrode side can be determined by appropriately changing the material and producing conditions of the structure constituting the surface (surface), and can be adjusted to obtain the desired value by performing any suitable surface treatment known in the related, for example, a physical treatment such as a corona discharge treatment, an oxygen plasma treatment, or an ultraviolet ozone treatment, a chemical treatment such as a cleaning treatment using water or organic solvent or an acid cleaning treatment, with respect to the structure constituting the surface.

The work function can be evaluated (measured) using, for example, a known Kelvin probe device in the related art (for example, FAC-2, available from RIKEN KEIKI Co., Ltd.) and gold (WF: 5.1 eV) as a reference sample for calibration.

As illustrated in FIG. 1, the light detecting element of the present embodiment may include a hole transport layer between the positive electrode and the active layer. The hole transport layer has a function of transporting holes from the active layer to the electrode. Since the hole transport layer has a function of blocking the flow of electrons to the electrode, it is sometimes called an electron block layer.

The hole transport layer provided in contact with the positive electrode may be particularly referred to as a hole injection layer. The hole transport layer (hole injection layer) provided in contact with the positive electrode has a function of promoting the injection of holes into the positive electrode.

The hole transport layer contains a hole transport material. Examples of the hole transport material include polythiophene and a derivative thereof, an aromatic amine compound, a polymer compound containing a constituent unit having an aromatic amine residue, CuSCN, CuI, NiO, and molybdenum oxide (MoO3).

The intermediate layer can be formed by the same coating method as that for the active layer.

The light detecting element according to the present embodiment is provided on a substrate, and preferably has a so-called reverse laminated structure in which the intermediate layer is an electron transport layer and a hole transport layer, and the negative electrode, the electron transport layer, the active layer, the hole transport layer, and the positive electrode are laminated in this order so as to be in contact with each other.

(Other)

The light detecting element of the present embodiment can be sealed by a sealing member such as a sealing substrate or a sealing material. Examples of the sealing member include a combination of cover glass having a recess and a sealing material.

The sealing member may have a layer structure of one or more layers. Therefore, as an example of the sealing member, a layer structure such as a gas barrier layer and a gas barrier film can be further exemplified.

The layer structure of the sealing member is preferably formed of a material having a property of blocking water (water vapor barrier property) or a property of blocking oxygen (oxygen barrier property). Examples of suitable materials as materials having a layer structure include organic materials such as resins of polyethylene trifluoride, polychlorotrifluoroethylene (PCTFE), polyimide, polycarbonate, polyethylene terephthalate, alicyclic polyolefin, and an ethylene-vinyl alcohol copolymer; and inorganic materials such as silicon oxide, silicon nitride, aluminum oxide, and diamond-like carbon.

According to the present invention, a thickness of the active layer is at least 800 nm, a weight ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material contained in the active layer is at most 99/1, and a work function of a surface in contact with the active layer on the negative electrode side is lower than an absolute value of a LUMO energy level of the n-type semiconductor material.

In the general photoelectric conversion element, in order to promote the extraction of electrons generated in the active layer, a difference between the work function of the surface in contact with the active layer on the negative electrode side and the LUMO energy level of the n-type semiconductor material contained in the active layer is set to be a positive value.

However, in the present invention, as described above, an appropriate energy barrier is provided at the interface of the active layer on the negative electrode side to prevent electrons from being taken out to the negative electrode.

As a result, the electrons are accumulated in the vicinity of the interface of the active layer on the negative electrode side, and the accumulated electrons disappear due to recombination with holes.

On the other hand, the electrons generated at a wavelength at which the light absorption of the active layer is low can be taken out to the negative electrode without being accumulated at the interface due to the low electron density.

As a result, the external quantum efficiency caused by the p-type semiconductor material and the n-type semiconductor material is reduced, and the external quantum efficiency has, for example, a narrow peak in the near infrared wavelength region, so that a light detecting element having a specific narrow band sensitivity characteristics can be realized in the near infrared wavelength region.

In the present embodiment, specifically, the full width at half maximum of the mountain-shaped peak of the external quantum efficiency generated in the near infrared wavelength region is obtained under the condition that a bias voltage of −2 V is applied to the light detecting element. Since the full width at half maximum can enhance the selectivity of the absorption wavelength, it is preferably less than at most 300 nm, and more preferably 100 nm or less.

With such a configuration, it is possible to provide a light detecting element having high sensitivity in a predetermined wavelength region, specifically, for example, a near infrared wavelength region, with a simpler configuration without using an optical member such as an optical film.

<Application Example of Light Detecting Element>

The light detecting element according to the embodiment of the present invention described above is suitably applied to a detector provided in various electronic devices such as a workstation, a personal computer, a personal digital assistant, an access control system, a digital camera, and a medical device.

The light detecting element of the present invention can be suitably applied to, for example, an image detector (image sensor) for a solid-state imaging device such as an X-ray imaging device and a CMOS image sensor; a detector that detects a predetermined feature of a part of a living body such as a fingerprint detector, a face detector, a vein detector, and an iris detector; and a detector of an optical biosensor such as a pulse oximeter, which are included in the above-exemplified electronic device.

Hereinafter, among the detectors to which the light detecting element according to the embodiment of the present invention can be suitably applied, configuration examples of the image detector for a solid-state imaging device and the fingerprint detector for a biometric information authentication device (fingerprint authenticating device) will be described with reference to the drawings.

<Image Detector>

FIG. 2 is a diagram schematically illustrating a configuration example of an image detector for a solid-state imaging device.

An image detector 1 is provided with a CMOS transistor substrate 20, an interlayer insulating film 30 provided so as to cover the CMOS transistor substrate 20, and a light detecting element 10 according to the embodiment of the present invention, provided on the interlayer insulating film 30, an interlayer wiring portion 32 that is provided so as to penetrate the interlayer insulating film 30 and electrically connects the CMOS transistor substrate 20 and the light detecting element 10 to each other, a sealing layer 40 provided so as to cover the light detecting element 10, and a color filter 50 provided on the sealing layer.

The CMOS transistor substrate 20 includes any suitable configuration known in the related art in an aspect corresponding to the design.

The CMOS transistor substrate 20 includes a transistor, capacitors, and the like formed within the thickness of the substrate, and includes functional elements such as a CMOS transistor circuit (MOS transistor circuit) for realizing various functions.

Examples of the functional element include a floating diffusion, a reset transistor, an output transistor, and a selection transistor.

A signal readout circuit and the like are built in the CMOS transistor substrate 20 by such functional elements and wiring.

The interlayer insulating film 30 can be formed of any suitable insulating material known in the related art such as silicon oxide or an insulating resin. The interlayer wiring portion 32 can be formed of, for example, any suitable conductive material (wiring material) known in the related art such as copper and tungsten. The interlayer wiring portion 32 may be, for example, an in-hole wiring formed at the same time as the formation of the wiring layer, or an embedded plug formed separately from the wiring layer.

The sealing layer 40 can be formed of any suitable materials known in the related art under the conditions that the penetration of harmful substances such as oxygen and water that may functionally deteriorate the light detecting element 10 can be prevented or suppressed. The sealing layer 40 may be formed of the sealing substrate 17 described above.

As the color filter 50, for example, a primary color filter which is made of any suitable material known in the related art and which corresponds to the design of the image detector 1 can be used. Further, as the color filter 50, a complementary color filter capable of reducing the thickness as compared with the primary color filter can also be used. Examples of the complementary color filters include color filters that combine three types of (yellow, cyan, and magenta), three types of (yellow, cyan, and transparent), three types of (yellow, transparent, and magenta), and three types of (transparent, cyan, and magenta) can be used. Assuming that these are subject to the ability to generate color image data, any suitable arrangement can be made corresponding to the design of the light detecting element 10 and the CMOS transistor substrate 20.

The light received by the photoelectric conversion element (light detecting element) 10 via the color filter 50 is converted into an electric signal according to the amount of light received by the light detecting element 10, and is output as a light receiving signal, that is, an electric signal corresponding to an image pickup target, outside the light detecting element 10.

Next, the received light signal output from the light detecting element 10 is input to the CMOS transistor substrate 20 via the interlayer wiring portion 32, and is read out by the signal readout circuit built in the CMOS transistor substrate 20, and signal processing is performed by a further optional suitable known functional unit in the related art (not shown) so as to generate the image information based on the image target.

<Fingerprint Detector>

FIG. 3 is a diagram schematically illustrating a configuration example of a fingerprint detector integrated with the display device.

The display device 2 of a personal digital assistant is provided with a fingerprint detector 100 including the light detecting element 10 according to the embodiment of the present invention as a main component and a display panel unit 200 that is provided on the fingerprint detector 100, and displays a predetermined image.

In this configuration example, the fingerprint detector 100 is provided in a region that substantially coincides with a display region 200 a of the display panel unit 200. In other words, the display panel unit 200 is integrally laminated above the fingerprint detector 100.

In a case where the fingerprint detection is performed only in a part region of the display region 200 a, the fingerprint detector 100 may be provided corresponding to only the part region of the display region 200 a.

The fingerprint detector 100 includes the light detecting element 10 according to the embodiment of the present invention as a functional unit that performs an essential function. The fingerprint detector 100 can be provided with any suitable member known in the related art, such as a protection film (not shown), a support substrate, a sealing substrate, a sealing member, a barrier film, a bandpass filter, and an infrared cut film in an aspect corresponding to the design of obtaining desired characteristics. For the fingerprint detector 100, the configuration of the image detector as described above can also be adopted.

The light detecting element 10 may be included in any aspect within the display region 200 a. For example, a plurality of light detecting elements 10 may be arranged in a matrix.

As described above, the light detecting element 10 is provided on the support substrate 11 or the sealing substrate, and the support substrate 11 is provided with electrodes (positive electrode or negative electrode) in a matrix, for example.

The light received by the light detecting element 10 is converted into an electric signal according to the amount of light received by the photoelectric conversion element 10, and is output as a light receiving signal, that is, an electric signal corresponding to a captured fingerprint, outside the light detecting element 10.

In this configuration example, the display panel unit 200 is configured as an organic electroluminescence display panel (organic EL display panel) including a touch sensor panel. The display panel unit 200 may be configured of, for example, instead of the organic EL display panel, a display panel having an any suitable configuration known in the related art, such as a liquid crystal display panel including a light source such as a backlight.

The display panel unit 200 is provided on the fingerprint detector 100 as described above. The display panel unit 200 includes an organic electroluminescence element (organic EL element) 220 as a functional unit that performs an essential function. The display panel unit 200 may be further provided with any suitable substrate (support substrate 210 or sealing substrate 240) known in the related art, such as a glass substrate, a sealing member, a barrier film, a polarizing plate such as a circular polarizing plate, and any suitable member known in the related art, such as a touch sensor panel 230 in an aspect corresponding to the desired characteristics.

In the configuration example described above, the organic EL element 220 is used as a light source for pixels in the display region 200 a, and is also used as a light source for capturing a fingerprint in the fingerprint detector 100.

Here, an operation of the fingerprint detector 100 will be briefly described.

When performing fingerprint authentication, the fingerprint detector 100 detects a fingerprint using the light emitted from the organic EL element 220 of the display panel unit 200. Specifically, the light emitted from the organic EL element 220 passes through the component existing between the organic EL element 220 and the light detecting element 10 of the fingerprint detector 100, and is reflected by skin (finger surface) of the fingertips of the fingers placed so as to be in contact with the surface of the display panel unit 200 within the display region 200 a. At least a part of the light reflected by the finger surface passes through the components existing between them and is received by the photoelectric conversion element 10, and is converted into an electric signal corresponding to the amount of light received by the photoelectric conversion element 10. Then, image information about the fingerprint on the finger surface is formed of the converted electric signals.

The personal digital assistant provided with the display device 2 performs fingerprint authentication by comparing the obtained image information with the fingerprint data for fingerprint authentication recorded in advance by any suitable step known in the related art.

Since the light detecting element of the present embodiment has a narrow peak of external quantum efficiency particularly in the near infrared wavelength region, as compared with the light detecting element in the related art having sensitivity in a wide range of the visible light wavelength region, for example, during the operation, the influence of a disturbance factor such as light caused by the external environment can be made smaller, and the illuminance dependence on illumination is also small. Therefore, according to the light detecting element of the present embodiment, a clearer image can be stably obtained, and therefore, it can be particularly preferably applied to an image sensor including a fingerprint detector having the above configuration.

[2. Method for Producing Light Detecting Element]

The method for producing the light detecting element of the present embodiment is not particularly limited. The light detecting element can be produced by a forming method suitable for the material selected for forming each component.

Hereinafter, as an embodiment of the present invention, a method for producing a light detecting element provided on a substrate (support substrate) and having a configuration in which a negative electrode, an electron transport layer, an active layer, a hole transport layer, and a positive electrode are in contact with each other in this order will be described.

(Step of Preparing Substrate)

In this step, a support substrate provided with a negative electrode is prepared.

A method of providing the negative electrode on the support substrate is not particularly limited. The negative electrode can be formed, for example, by forming the above-exemplified material on the support substrate made of the materials as described above by a vacuum deposition method, a sputtering method, an ion plating method, a plating method, or the like.

Further, a substrate provided with a thin film formed of the material of the electrode as described above is available from the market, and if necessary, the negative electrode is formed by patterning a conductive thin film, thereby preparing a support substrate provided with the negative electrode.

(Step of Forming Electron Transport Layer)

A method for producing the light detecting element may include a step of forming an electron transport layer (electron injection layer) provided between the active layer and the negative electrode as an intermediate layer.

Specifically, the method for producing the light detecting element of the present embodiment may further include a step of forming an electron transport layer after the step of preparing a support substrate provided with a negative electrode and before a step of forming an active layer.

A method for forming an electron transport layer is not particularly limited. From the viewpoint of more simplifying the step of forming the electron transport layer, it is preferable to form the electron transport layer by a coating method. That is, it is preferable that before the formation of the active layer and after the formation of the negative electrode, a coating liquid containing an electron transport material and a solvent, which will be described later, is applied onto the negative electrode, and the solvent is removed, if necessary, by performing a drying treatment (heat treatment) so as to form the electron transport layer.

The electron transport material for forming the electron transport layer may be an organic compound or an inorganic compound.

The electron transport material which is an organic compound may be a low molecular weight organic compound or a high molecular weight organic compound.

Examples of the electron transport material that is a low molecular weight organic compound include an oxadiazole derivative, anthracinodimethane and a derivative thereof, benzoquinone and a derivative thereof, naphthoquinone and a derivative thereof, anthraquinone and a derivative thereof, tetracyanoanthraquinodimethane and a derivative thereof, a fluorenone derivative, diphenyldicyanoethylene and a derivative thereof, a diphenoquinone derivative, 8-hydroxyquinoline and a metal complex of derivative thereof, polyquinolin and a derivative thereof, polyquinoxaline and a derivative thereof, polyfluorene and a derivative thereof, fullerenes such as C60 fullerene and a derivative thereof, and a phenanthrene derivative such as bathocuproine.

Examples of the electron transport material which is the polymer organic compound include polyvinylcarbazole and a derivative thereof, polysilane and a derivative thereof, a polysiloxane derivative having an aromatic amine structure in a side chain or main chain, polyaniline and a derivative thereof, polythiophene and a derivative thereof, polypyrrole and a derivative thereof, polyphenylene vinylene and a derivative thereof, polythienylene vinylene and a derivative thereof, and polyfluorene and a derivative thereof.

Examples of the electron transport material that is an inorganic compound include zinc oxide, titanium oxide, zirconium oxide, tin oxide, indium oxide, GZO (gallium-doped zinc oxide), ATO (antimony-doped tin oxide), and AZO (aluminum-doped zinc oxide). Among these, zinc oxide, gallium-doped zinc oxide, or aluminum-doped zinc oxide is preferable. When forming the electron transport layer, it is preferable to form the electron transport layer by using a coating liquid containing granular zinc oxide, gallium-doped zinc oxide, or aluminum-doped zinc oxide. As such an electron transport material, it is preferable to use nanoparticles of zinc oxide, nanoparticles of gallium-doped zinc oxide, or nanoparticles of aluminum-doped zinc oxide, and it is more preferable to form the electron transport layer using an electron transport material consisting only of nanoparticles of zinc oxide, nanoparticles of gallium-doped zinc oxide, or nanoparticles of aluminum-doped zinc oxide.

The sphere-equivalent average particle size of the nanoparticles of zinc oxide, the nanoparticles of the gallium-doped zinc oxide, and the nanoparticles of aluminum-doped zinc oxide is preferably 1 nm to 1000 nm and more preferably 10 nm to 100 nm. The average particle size can be measured by, for example, a laser light scattering method and an X-ray diffraction method.

In the method for producing a light detecting element of the present embodiment, a step of forming an electron transport layer preferably includes a step of forming an electron transport layer by applying a coating liquid containing PEIE and zinc oxide.

Examples of the solvent contained in the coating liquid containing the electron transport material include water, alcohol, ketone, and hydrocarbon. Specific examples of the alcohol include methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol, butoxyethanol, and methoxybutanol. Specific examples of the ketone include acetone, methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, and cyclohexanone. Specific examples of the hydrocarbon include n-pentane, cyclohexane, n-hexane, benzene, toluene, xylene, tetralin, chlorobenzene, and orthodichlorobenzene. The coating liquid may contain one kind of solvent alone, may contain two or more kinds of solvents, and may contain two or more kinds of the above-described solvents.

The coating liquid used in the coating method for forming the electron transport layer may be a dispersion liquid such as an emulsion (emulsion liquid) or a suspension (suspension). The coating liquid is preferably a coating liquid that causes less damage to the layer (active layer, or the like) to which the coating liquid is applied, and specifically, a coating liquid that is difficult to dissolve the layer (active layer, or the like) to which the coating liquid is applied.

The step of forming the electron transport layer is performed by a coating method, and by adjusting the size (particle size, molecular weight, or the like in a case of a polymer compound) of the electron transport material to be used, the work function of the surface in contact with the active layer of the electron transport layer can be adjusted to any suitable range. Further, in a case where the coating method is the spin coating method, the work function of the surface of the electron transport layer in contact with the active layer can be adjusted to any suitable range by adjusting the characteristics of the coating liquid such as the concentration of the components in the coating liquid used (viscosity of the coating liquid) and the implementation conditions such as the spin rotation speed, the rotation time, and the drying (heating) conditions.

(Step of Forming Active Layer)

The active layer, which is a main component of the photoelectric conversion element of the present embodiment, can be produced by a coating method using a coating liquid (ink).

Hereinafter, a step (i) and a step (ii) included in the step of forming the active layer, which is a main component of the photoelectric conversion element of the present invention, will be described.

(Step (i))

As a method for applying a coating liquid to a coating target, any suitable coating method can be used.

As the coating method, a slit coating method, a knife coating method, a spin coating method, a micro gravure coating method, a gravure coating method, a bar coating method, an ink jet printing method, a nozzle coating method, or a capillary coating method is preferable, and the slit coating method, the spin coating method, the capillary coat method, or the bar coat method is more preferable, and the slit coat method or the spin coating method is further preferable.

A coating liquid for forming an active layer is applied to a coating target selected according to the photoelectric conversion element and the producing method thereof. The coating liquid for forming an active layer can be applied to the functional layer of the photoelectric conversion element, in which the active layer can exist, in the step of producing the photoelectric conversion element. Therefore, the coating target of the coating liquid for forming an active layer differs depending on the layer configuration of the photoelectric conversion element to be produced and the order of layer formation. For example, in a case where it has a layer configuration in which the photoelectric conversion element is provided on the substrate, and the positive electrode, the hole transport layer, the active layer, the electron transport layer, and the negative electrode are laminated, and the layer described on the right side is formed first, the coating target of the coating liquid for forming an active layer is the electron transport layer. In addition, in a case where it has a layer configuration in which the photoelectric conversion element is provided on the substrate, and the negative electrode, the electron transport layer, the active layer, the hole transport layer, and the positive electrode are laminated, and the layer described on the right side is formed first, the coating target of the coating liquid for forming an active layer is the hole transport layer.

(Step (ii))

Any suitable method can be used as a method for removing the solvent from the coating film of the coating liquid, that is, a method for removing the solvent and solidifying the coating film. Examples of the method for removing the solvent include a method for direct heating using a hot plate, and a drying method such as a hot air drying method, an infrared heating drying method, a flash lamp annealing drying method, and a vacuum drying method.

The thickness of the active layer can be set to a desired thickness by appropriately adjusting the solid content concentration in the coating liquid and the conditions of the above step (i) and/or step (ii).

Specifically, for example, in a case where the coating method is the knife coating method, the thickness of the active layer can be adjusted to an any suitable thickness by adjusting the characteristic conditions of the coating liquid such as the concentration (viscosity of the coating liquid) of the components in the coating liquid to be used, and various implementation conditions in the knife coater method.

For example, in order to adjust the thickness of the active layer in the direction of increasing the thickness, the concentration of the component in the coating liquid is more increased and/or a gap between the surface to be coated and the blade of the knife in the knife coating method may be widened so that the coating speed is more increased.

The step of forming the active layer may include other steps in addition to the steps (i) and (ii), provided that the object and effect of the present invention are not impaired.

The method for producing the light detecting element may be a method for producing a light detecting element including a plurality of active layers, or a method in which the steps (i) and (ii) are repeated a plurality of times.

The coating liquid for forming an active layer may be a solution, or may be a dispersion liquid such as a dispersion liquid, an emulsion (emulsion liquid), or a suspension (suspension). The coating liquid for forming an active layer according to the present embodiment contains a p-type semiconductor material, an n-type semiconductor material, and a solvent. Hereinafter, the components of the coating liquid for forming an active layer will be described.

(p-type semiconductor material)

The p-type semiconductor material may be a low molecular weight compound or a polymer compound.

Examples of the p-type semiconductor material which is the low molecular weight compound include phthalocyanine, metallic phthalocyanine, porphyrin, metallic porphyrin, oligothiophene, tetracene, pentacene, and rubrene.

In a case where the p-type semiconductor material is a polymer compound, the polymer compound has a predetermined polystyrene-equivalent weight average molecular weight.

Here, the polystyrene-equivalent weight average molecular weight means a weight average molecular weight calculated using a standard polystyrene sample using gel permeation chromatography (GPC).

The polystyrene-equivalent weight average molecular weight of the p-type semiconductor material is preferably 20000 or more and 200000 or less, more preferably 30000 or more and 180000 or less, and further preferably 40000 or more and 150000 or less from the viewpoint of solubility in a solvent.

Examples of the p-type semiconductor material which is the polymer compound include polyvinylcarbazole and a derivative thereof, polysilane and a derivative thereof, a polysiloxane derivative having an aromatic amine structure in a side chain or main chain, polyaniline and a derivative thereof, polythiophene and a derivative thereof, polypyrrole and a derivative thereof, polyphenylene vinylene and a derivative thereof, polythienylene vinylene and a derivative thereof, and polyfluorene and a derivative thereof.

The p-type semiconductor material, which is the polymer compound, is preferably a polymer compound containing a constituent unit having a thiophene skeleton.

The p-type semiconductor material is preferably a polymer compound containing a constituent unit represented by the following Formula (I) and/or a constituent unit represented by the following Formula (II).

In Formula (I), Ar¹ and Ar² represent trivalent aromatic heterocyclic groups, and Z represents groups represented by the following Formulas (Z-1) to (Z-7).

[Chem. 4]

—Ar³—  (II)

In Formula (II), Ar³ represents a divalent aromatic heterocyclic group.

In Formulas (Z-1) to (Z-7), R is a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a monovalent heterocyclic group, a substituted amino group, an acyl group, an imine residue, an amide group, an acidimide group, a substituted oxycarbonyl group, an alkenyl group, an alkynyl group, a cyano group, or a nitro group. In a case where there are two Rs in each of the Formulas (Z-1) to (Z-7), the two Rs may be the same or different from each other.

The constituent unit represented by Formula (I) is preferably the constituent unit represented by the following Formula (I-1).

In Formula (I-1), Z has the same meaning as described above.

Examples of the constituent unit represented by Formula (I-1) include constituent units represented by the following Formulas (501) to (505).

In the Formulas (501) to (505), R has the same meaning as described above. In a case where there are two Rs, the two Rs may be the same or different from each other.

The number of carbon atoms of the divalent aromatic heterocyclic group represented by Ar³ is usually 2 to 60, preferably 4 to 60, and more preferably 4 to 20. The divalent aromatic heterocyclic group represented by Ar³ may have a substituent. Examples of substituents that the divalent aromatic heterocyclic group represented by Ar³ may have include a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a monovalent heterocyclic group, a substituted amino group, an acyl group, an imine residue, an amide group, an acidimide group, a substituted oxycarbonyl group, an alkenyl group, an alkynyl group, a cyano group, and a nitro group.

Examples of the divalent aromatic heterocyclic group represented by Ara include groups represented by the following Formulas (101) to (185).

In the Formulas (101) to (185), R has the same meaning as described above. In a case where there are a plurality of Rs, the plurality of Rs may be the same or different from each other.

As the constituent unit represented by the Formula (II), constituent units represented by the following Formulas (II-1) to (II-6) are preferable.

In Formulas (II-1) to (II-6), X¹ and X² each independently represent an oxygen atom or a sulfur atom, and R has the same meaning as described above. In a case where there are a plurality of Rs, the plurality of Rs may be the same or different from each other.

From the viewpoint of availability of the raw material compound, it is preferable that both X¹ and X² in the Formulas (II-1) to (II-6) are sulfur atoms.

The polymer compound which is the p-type semiconductor material may have two or more kinds of constituent units of Formula (I), and may have two or more kinds of constituent units of Formula (II).

In order to improve the solubility in the solvent, the polymer compound which is the p-type semiconductor material may have a constituent unit represented by the following Formula (III).

[Chem. 13]

—Ar⁴—  (III)

In Formula (III), Ar⁴ represents an arylene group.

The arylene group represented by Ar⁴ means a remaining atomic group obtained by removing two hydrogen atoms from the aromatic hydrocarbon which may have a substituent. Aromatic hydrocarbons also include compounds in which two or more selected from the group consisting of a compound having a fused ring, an independent benzene ring, and a fused ring are bonded directly or via a divalent group such as a vinylene group.

Examples of the substituents that the aromatic hydrocarbon may have include the same substituents as those exemplified as the substituents that the heterocyclic compound may have.

The number of carbon atoms in a portion of the arylene group excluding the substituent is usually 6 to 60, and preferably 6 to 20. The number of carbon atoms of the arylene group including the substituent is usually about 6 to 100.

Examples of the arylene group include a phenylene group (for example, the following Formulas 1 to 3), a naphthalene-diyl group (for example, the following Formulas 4 to 13), an anthracene-diyl group (for example, the following Formulas 14 to 19), a biphenyl-diyl group (for example, the following Formulas 20 to 25), a terphenyl-diyl group (for example, the following Formulas 26 to 28), a fused ring compound group (for example, the following Formulas 29 to 35), a fluorene-diyl group (for example, the following Formulas 36 to 38), and a benzofluorene-diyl group (for example, the following Formulas 39 to 46).

In Formulas 1 to 46, R has the same meaning as described above. In a case where there are a plurality of Rs, the plurality of Rs may be the same or different from each other.

The constituent unit constituting the polymer compound, which is a p-type semiconductor material, may be a constituent unit in which two or more types selected from the constituent unit represented by Formula (I), the constituent unit represented by Formula (II), and the constituent unit represented by Formula (III) are combined and connected to each other.

In a case where the polymer compound as a p-type semiconductor material has the constituent unit represented by Formula (I) and/or the constituent unit represented by Formula (II), assuming that the amount of all the constituent units contained in the polymer compound is 100 mol %, the total amount of the constituent unit represented by Formula (I) and the constituent unit represented by Formula (II) is usually 20 to 100 mol %, and in order to improve charge transport properties as a p-type semiconductor material, it is preferably 40 to 100 mol %, and more preferably 50 to 100 mol %.

Specific examples of the polymer compound as a p-type semiconductor material include polymer compounds represented by the following Formulas P-1 to P-6 (polymer compound P-1 to polymer compound P-6).

The coating liquid for forming an active layer may contain only one type of p-type semiconductor material, or may contain two or more types in optional ratio combination.

As a p-type semiconductor material, the polymer compound P-1 as described above is preferably used from the viewpoint that a light detecting element having a narrow band sensitivity characteristic having a narrow peak in the EQE spectrum with a small full width at half maximum (FWHM) can be realized particularly in the near infrared wavelength region.

(n-Type Semiconductor Material)

The n-type semiconductor material is preferably a fullerene derivative. The fullerene derivative means a compound in which at least a part of fullerene (C60 fullerene, C70 fullerene, and C84 fullerene) is modified.

Examples of fullerene derivatives include compounds represented by the following Formulas (N-1) to (N-4).

In Formulas (N-1) to (N-4), R^(a) represents an alkyl group, an aryl group, a monovalent heterocyclic group, or a group having an ester structure. A plurality of R^(a)s may be the same or different from each other.

R^(b) represents an alkyl group or an aryl group. A plurality of R^(b)s may be the same or different from each other.

Examples of the group having an ester structure represented by R^(a) include a group represented by the following Formula (19).

In Formula (19), u1 represents an integer from 1 to 6. u2 represents an integer from 0 to 6. R^(c) represents an alkyl group, an aryl group, or a monovalent heterocyclic group.

Examples of C₆₀ fullerene derivatives include the following compounds.

Specific suitable examples of the C₆₀ fullerene derivative include [6,6]-phenyl-C61 butyric acid methyl ester (C60PCBM, [6,6]-Phenyl-C61 butyric acid methyl ester), and bisphenyl-C61 methyl butyrate (bisadduct of phenyl C61-butyric acid methyl ester)

Specific examples of the C70 fullerene derivative include compounds represented by the following formula.

Suitable specific examples of the C₇₀ fullerene derivative include [6,6]-phenyl-C71 butyric acid methyl ester (C70PCBM, [6,6]-phenyl-C71-butyric acid methyl ester), and inden C70 propionic acid hexyl ester (C70IPH, indene-C70-propionic acid hexyl ester).

As an n-type semiconductor material, C70PCBM, which is a C₇₀ fullerene derivative is preferably used from the viewpoint that a light detecting element having a narrow band sensitivity characteristic having a narrow peak in the EQE spectrum with a small full width at half maximum (FWHM) can be realized only in the near infrared wavelength region.

Specific examples of the C₈₄ fullerene derivative include [6,6] phenyl-C85 butyric acid methyl ester (C84PCBM, [6,6]-Phenyl C85 butyric acid methyl ester).

The coating liquid for forming an active layer may contain only one type of n-type semiconductor material, or may contain two or more types in optional ratio combination.

(Solvent)

The coating liquid for forming an active layer may contain only one type of solvent, or may contain two or more types in optional ratio combination. In a case where the coating liquid for forming an active layer contains two or more kinds of solvents, the main solvent (referred to as a first solvent), which is the main component, and other additive solvents (referred to as a second solvent) added to improve the solubility are preferably contained. The first solvent and the second solvent will be described below.

(1) First Solvent

The solvent can be selected in consideration of the solubility in the selected p-type semiconductor material and the n-type semiconductor material, and the characteristics (boiling point, and the like) for corresponding to the drying conditions when forming the active layer.

The first solvent as the main solvent is preferably aromatic hydrocarbon (hereinafter, simply referred to as an aromatic hydrocarbon) which may have a substituent (alkyl group or halogen atom). The first solvent is preferably selected in consideration of the solubility of the selected p-type semiconductor material and n-type semiconductor material.

Examples of such aromatic hydrocarbons include toluene, xylene (for example, o-xylene, m-xylene, and p-xylene), trimethylbenzene (for example, mesitylene, 1,2,4-trimethylbenzene (psoidoctene)), butylbenzene (for example, n-butylbenzene, sec-butylbenzene, and tert-butylbenzene), methylnaphthalene (for example, 1-methylnaphthalene), tetralin, indan, chlorobenzene, and dichlorobenzene (o-dichlorobenzene).

The first solvent may be formed of only one type of aromatic hydrocarbon or may be formed of two or more types of aromatic hydrocarbons. The first solvent is preferably formed of only one aromatic hydrocarbon.

The first solvent is preferably one or more selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene, pseudocumene, n-butylbenzene, sec-butylbenzene, tert-butylbenzene, methylnaphthalene, tetralin, indan, chlorobenzene, and o-dichlorobenzene, and more preferably o-xylene, pseudocumene, chlorobenzene, or o-dichlorobenzene.

(2) Second Solvent

The second solvent is preferably a solvent selected from the viewpoint of facilitating the implementation of the producing step and further improving the characteristics of the light detecting element. Examples of the second solvent include a ketone solvent such as acetone, methyl ethyl ketone, cyclohexanone, acetophenone, and propiophenone, and an ester solvent such as ethyl acetate, butyl acetate, phenyl acetate, ethyl cell solve acetate, methyl benzoate, butyl benzoate, and benzyl benzoate.

As the second solvent, acetophenone, propiophenone, or benzyl benzoate is preferable.

(3) Combination of First Solvent and Second Solvent

Suitable combinations of the first solvent and the second solvent include, for example, a combination of o-xylene and acetophenone.

(4) Weight Ratio of First Solvent and Second Solvent

The weight ratio (first solvent:second solvent) of the first solvent, which is the main solvent, to the second solvent, which is the additional solvent, is preferably in the range of 85:15 to 99:1 from the viewpoint of further improving the solubility of the p-type semiconductor material and the n-type semiconductor material.

(5) Total Weight Percentage of First Solvent and Second Solvent

When the entire weight of the coating liquid is 100% by weight, the total weight of the first solvent and the second solvent contained in the coating liquid is preferably 90% by weight or more, more preferably 92% by weight or more, and further preferably 95% by weight or more from the viewpoint of further improving the solubility of the p-type semiconductor material and the n-type semiconductor material, and it is preferably 99% by weight or less, more preferably 98% by weight or less, and further preferably 97.5% by weight or less from the viewpoint of increasing the concentration of the p-type semiconductor material and the n-type semiconductor material in the coating liquid so as to facilitate the formation of a layer having a certain thickness or more.

(6) Other Optional Solvents

The solvent may contain any solvent other than the first solvent and the second solvent. When the total weight of all the solvents contained in the coating liquid is 100% by weight, the content of other optional solvents is preferably 5% by weight or less, more preferably 3% by weight or less, and further preferably 1% by weight or less. As other optional solvents, solvents having a boiling point higher than that of the second solvent are preferable.

(Optional Components)

In addition to the first solvent, the second solvent, the p-type semiconductor material, and the n-type semiconductor material, the coating liquid may contain optional components such as an ultraviolet absorber, an antioxidant, a sensitizer for sensitizing the function of generating electric charges by the generated light, and a light stabilizer for increasing the stability from ultraviolet rays as long as the object and effect of the present invention are not impaired.

(Concentration of p-Type Semiconductor Material and n-Type Semiconductor Material in Coating Liquid)

The total concentration of the p-type semiconductor material and the n-type semiconductor material in the coating liquid is preferably 0.01% by weight or more and 20% by weight or less, more preferably 0.01% by weight or more and 10% by weight or less, further preferably 0.01% by weight or more and 5% by weight or less, and particularly preferably 0.1% by weight or more and 5% by weight or less. The p-type semiconductor material and the n-type semiconductor material may be dissolved or dispersed in the coating liquid. The p-type semiconductor material and the n-type semiconductor material are preferably at least partially dissolved, and more preferably all are dissolved.

(Preparation of Coating Liquid)

The coating liquid can be prepared by a known method. For example, coating liquid can be prepared by a method for mixing the first solvent and the second solvent are mixed to prepare a mixed solvent and adding the p-type semiconductor material and the n-type semiconductor material to the mixed solvent, and a method for adding the p-type semiconductor material to the first solvent, adding the n-type semiconductor material to the second solvent, and then mixing the first solvent and the second solvent to which each material has been added.

The first solvent, the second solvent, the p-type semiconductor material, and the n-type semiconductor material may be heated and mixed to a temperature equal to or lower than the boiling point of the solvent.

After mixing the first solvent, the second solvent, the p-type semiconductor material, and the n-type semiconductor material, the obtained mixture may be filtered using a filter, and the obtained filtrate may be used as a coating liquid. As the filter, for example, a filter formed of a fluororesin such as polytetrafluoroethylene (PTFE) can be used.

(Step of Forming Positive Electrode)

In this step, a positive electrode is formed on the active layer. In the present embodiment, the positive electrode is formed on the active layer; however, in a case where the method for producing the photoelectric conversion element includes a step of forming a hole transport layer which is an intermediate layer between the positive electrode and the active layer, the positive electrode is formed on the hole transport layer (hole injection layer).

The method for forming a positive electrode is not particularly limited. The positive electrode can be formed on the layer on which the positive electrode should be formed by forming the electrode material as described above using a vacuum deposition method, a sputtering method, an ion plating method, a plating method, a coating method, or the like.

In a case where the material of the positive electrode is polyaniline and a derivative thereof, polythiophene and a derivative thereof, nanoparticles of the conductive substance, nanowire of the conductive substance, or nanotube of the conductive substance, a negative electrode can be formed using an emulsion (emulsion), suspension (suspension), or the like containing these materials and a solvent by a coating method.

In a case where the positive electrode is formed by the coating method, the positive electrode can be formed by using a coating liquid containing a conductive substance, a metal ink, a metal paste, a low melting point metal in a molten state, or the like. Examples of the coating method of the coating liquid containing the material of the positive electrode and the solvent include the same method as that in the step of forming the active layer as described above.

Examples of the solvent contained in the coating liquid used when forming the positive electrode by the coating method include a hydrocarbon solvent such as toluene, xylene, mesitylene, tetraline, decalin, bicyclohexyl, n-butylbenzene, sec-butylbezen, and tert-butylbenzene; a halogenized saturated hydrocarbon solvent such as carbon tetrachloride, chloroform, dichloromethane, dichloroethane, chlorobutane, bromobutane, chloropentane, bromopentane, chlorohexane, bromohexane, chlorocyclohexane, and bromocyclohexane; a halogenated unsaturated hydrocarbon solvent such as chlorobenzene, dichlorobenzene, and trichlorobenzene; an ether solvent such as tetrahydrofuran and tetrahydropyran; water; and alcohol. Specific examples of the alcohol include methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol, butoxyethanol, and methoxybutanol. The coating liquid may contain one kind of solvent alone, may contain two or more kinds of solvents, and may contain two or more kinds of the above-described solvents.

(Step of Forming Hole Transport Layer)

The method for forming a hole transport layer in a case of forming the hole transport layer (hole injection layer) is not particularly limited. From the viewpoint of more simplifying the step of forming the hole transport layer, it is preferable to form the hole transport layer by a coating method. The hole transport layer can be formed, for example, by applying a coating liquid containing the material and solvent of the hole transport layer as described above onto the active layer.

Examples of the solvent in the coating liquid used in the coating method include water, alcohol, ketone, and hydrocarbon. Specific examples of the alcohol include methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol, butoxyethanol, and methoxybutanol. Specific examples of the ketone include acetone, methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, and cyclohexanone. Specific examples of the hydrocarbons include n-pentane, cyclohexane, n-hexane, benzene, toluene, xylene, tetralin, chlorobenzene, and orthodichlorobenzene. The coating liquid may contain one kind of solvent alone, may contain two or more kinds of solvents, and may contain two or more kinds of the above-exemplified solvents. The amount of the solvent in the coating liquid is preferably 1 part by weight or more and 10000 parts by weight or less, and more preferably 10 parts by weight or more and 1000 parts by weight or less with respect to 1 part by weight of the material of the hole transport layer.

Examples of the method (coating method) for applying the coating liquid containing the material of the hole transport layer and the solvent include a spin coating method, a knife coating method, a casting method, a micro gravure coating method, a gravure coating method, and a bar coating method. Examples thereof include a roll coating method, a wire bar coating method, a dip coating method, a spray coating method, a screen printing method, a flexographic printing method, an offset printing method, an ink jet printing method, a dispenser printing method, a nozzle coating method, and a capillary coating method. Among these, the spin coating method, the flexographic printing method, the ink jet printing method, and the dispenser printing method are preferable.

It is preferable to remove the solvent from the coating film by subjecting the coating film obtained by applying the coating liquid containing the material of the hole transport layer and the solvent to a heat treatment, an air-drying treatment, a reduced pressure treatment, or the like.

(Step of Forming Positive Electrode)

In this embodiment, the positive electrode is usually formed on the active layer. In a case where the method for producing the light detecting element according to the present embodiment includes a step of forming a hole transport layer, the positive electrode is formed on the hole transport layer.

The method for forming a positive electrode is not particularly limited. The positive electrode can be formed on the layer such as the active layer and the hole transport layer, on which the positive electrode should be formed, by forming the material as described above using a vacuum deposition method, a sputtering method, an ion plating method, a plating method, a coating method, or the like.

In a case where the material of the positive electrode is polyaniline and a derivative thereof, polythiophene and a derivative thereof, nanoparticles of the conductive substance, nanowire of the conductive substance, or nanotube of the conductive substance, the positive electrode can be formed using an emulsion (emulsion), suspension (suspension), or the like containing these materials and a solvent by a coating method.

In a case where the material of the positive electrode contains a conductive substance, the positive electrode can be formed by using a coating liquid containing a conductive substance, a metal ink, a metal paste, a low melting point metal in a molten state, or the like. Examples of the coating method of the coating liquid containing the material of the positive electrode and the solvent include the same method as that in the step of forming the active layer as described above.

Examples of the solvent contained in the coating liquid used when forming the positive electrode by the coating method include a hydrocarbon solvent such as toluene, xylene, mesitylene, tetraline, decalin, bicyclohexyl, n-butylbenzene, sec-butylbenzen, and tert-butylbenzene; a halogenized saturated hydrocarbon solvent such as carbon tetrachloride, chloroform, dichloromethane, dichloroethane, chlorobutane, bromobutane, chloropentane, bromopentane, chlorohexane, bromohexane, chlorocyclohexane, and bromocyclohexane; a halogenated aromatic hydrocarbon solvent such as chlorobenzene, dichlorobenzene, and trichlorobenzene; an ether solvent such as tetrahydrofuran and tetrahydropyran; water; and alcohol. Specific examples of the alcohol include methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol, butoxyethanol, and methoxybutanol. The coating liquid may contain one kind of solvent alone, may contain two or more kinds of solvents, and may contain two or more kinds of the above-described solvents.

EXAMPLES

Hereinafter, examples will be described in order to explain the present invention in more detail. The present invention is not limited to the examples described below.

Example 1

(1) Producing of Light Detecting Element

A glass substrate having an ITO thin film (negative electrode) formed with a thickness of 150 nm was prepared by a sputtering method, and a surface of the glass substrate was subjected to an ozone UV treatment.

Next, a solution obtained by diluting polyethyleneimine ethoxylate (PEIE) (available from Aldrich, trade name: polyethyleneimine, 80% ethoxylated solution, weight average molecular weight 110000), which is a modified product containing polyethyleneimine as a main chain and ethylene oxide added to a nitrogen atom in the main chain 100 times with water was used as a coating liquid, and the coating liquid was applied by a spin coating method on a glass substrate on which a negative electrode was formed. The glass substrate coated with the coating liquid was heated at 120° C. for 10 minutes using a hot plate to form the electron transport layer 1 containing PEIE on the ITO thin film, which is the negative electrode. The thickness of the electron transport layer 1 was 1 nm. The work function of the electron transport layer 1 formed here was measured (details will be described later).

Next, a polymer compound P-1 as a p-type semiconductor material and C60PCBM (available from Frontier Carbon Co., Ltd., trade name: E100, LUMO level: −4.3 eV) as an n-type semiconductor material were mixed at a weight ratio of 1/2 (p/n ratio), and the mixture was added to a mixed solvent of o-xylene as the first solvent and acetophenone as the second solvent (o-xylene:acetophenone=95:5 (weight ratio)), and stirred at 80° C. for 10 hours to prepare a coating liquid for forming an active layer.

The prepared coating liquid for forming an active layer was applied onto the electron transport layer of a glass substrate by the knife coater method, and the obtained coating film was dried for 5 minutes using a hot plate heated to 100° C. to form an active layer. The thickness of the formed active layer was 800 nm.

Next, in a resistance heating vapor deposition apparatus, molybdenum oxide (MoO₃) was deposited as a hole transport layer on the formed active layer to a thickness of about 30 nm, and a silver (Ag) layer was further formed as a positive electrode with a thickness of about 80 nm, thereby producing a light detecting element (photoelectric conversion element).

Next, a UV curable sealant was applied on a glass substrate around the produced light detecting element, the glass substrate which is the sealing substrate is bonded, and then UV light is emitted to seal the light detecting element. The planar shape of the obtained light detecting element when viewed from the thickness direction was a square of 2 mm×2 mm.

(2) Evaluation of Characteristics of Light Detecting Element

The external quantum efficiency (EQE) was measured using a spectral sensitivity measuring device (CEP-2000, available from Bunkoukeiki Co., Ltd) with a bias voltage of −2 V applied to the produced light detecting element. The full width at half maximum (FWHM) of the peak located on the longest wavelength region of the EQE spectrum was calculated. Specifically, as for the full width at half maximum, when the value of the peak located on the longest wavelength region of the measured EQE spectrum peaks was set to 100% peak sensitivity, a peak width (wavelength width) corresponding to the peak sensitivity of 50% at the same peak was calculated as the full width at half maximum. The results are indicated in Table 1.

As a result, such a peak was a narrow peak located in near infrared wavelength region with a full width at half maximum (FWHM) of 60 nm. That is, it was found that the light detecting element of Example 1 has a narrow band sensitivity characteristic in the near infrared region.

(3) Evaluation of LUMO of n-Type Semiconductor Material Contained in Active Layer)

A LUMO level of the n-type semiconductor material was estimated from cyclic voltammetry (CV) measurement values.

Specifically, LUMO of C60 PCBM, which is an n-type semiconductor material, was measured using a CV measuring device (Electrochemical Analyzer Model 600B, available from BAS), by setting a dehydrated acetonitrile solution containing tetrabutylammonium hexafluorophosphate (TBAPF6, available from Aldrich) as a support electrolyte at a concentration of 0.1 M, a film formed by dropping an n-type semiconductor material dissolved in chloroform on platinum foil as a work electrode, platinum foil as a counter electrode, an Ag/AgCl electrode as a reference electrode, and a ferrocene potential as a standard potential. The LUMO of the obtained C60PCBM was −4.3 eV.

(4) Evaluation of Work Function (WF, eV) of Surface in Contact with Active Layer

As described above, the work function of the electron transport layer 1 was evaluated using a Kelvin probe device using a glass substrate after the electron transport layer was formed as described above. As the Kelvin probe device, FAC-2 available from RIKEN KEIKI Co., Ltd. was used. Gold (WF: 5.1 eV) was used as a reference sample for calibration. The work function of the obtained electron transport layer was 4.2 eV.

Examples 2 and 3

A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that the thickness of the active layer was set to 1000 nm (Example 2) and 1200 nm (Example 3). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1.

Comparative Example 1

A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that the thickness of the active layer was set to 550 nm. The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1.

Examples 4 and 5

A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that an electron transport layer 2 having a thickness of 30 nm and containing zinc oxide was formed by using a zinc oxide dispersion liquid (available from TAYCA Corporation, trade name: HTD-711Z), and the thickness of the active layer was set to 1100 nm (Example 4) and 1400 nm (Example 5). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1. The WF of electron transport layer 2 was 4.2 eV.

Comparative Examples 2 and 3

A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that an electron transport layer 2 having a thickness of 30 nm and containing zinc oxide was formed by using a zinc oxide dispersion liquid (available from TAYCA Corporation, trade name: HTD-711Z), and the thickness of the active layer was set to 650 nm (Comparative Example 2) and 750 nm (Comparative Example 3). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1. The WF of electron transport layer 2 was 4.2 eV.

Comparative Examples 4 to 12

A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that an electron transport layer 3 having a thickness of 30 nm and containing zinc oxide was formed by using a zinc oxide dispersion liquid (available from Avantama, trade name: N-10), and the thickness of the active layer was set to 600 nm (Comparative Example 4), 800 nm (Comparative Example 5), 850 nm (Comparative Example 6), 950 nm (Comparative Example 7), 1100 nm (Comparative Example 8), 1400 nm (Comparative Example 9), 1800 nm (Comparative Example 10), 3000 nm (Comparative Example 11), and 3500 nm (Comparative Example 12). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1. The WF of electron transport layer 3 was 4.4 eV.

Comparative Examples 13 to 16

A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that an electron transport layer 4 having a thickness of 30 nm and containing titanium oxide was formed by using a titanium (IV) isopropoxide solution (available from Aldrich), and the thickness of the active layer was set to 550 nm (Comparative Example 13), 1000 nm (Comparative Example 14), 1300 nm (Comparative Example 15), and 3200 nm (Comparative Example 16). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1. The WF of electron transport layer 4 was 4.7 eV.

Comparative Examples 17 to 20

A film having a thickness of 30 nm and containing zinc oxide was formed using a solution of zinc oxide dispersion liquid (available from TAYCA Corporation, trade name: HTD-711Z) diluted 10 times with 3-pentanol. An electron transport layer 5 was obtained by subjecting the formed film to a UV ozone treatment for 2 minutes. A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that the obtained electron transport layer 5 was used, and the thickness of the active layer was set to 1000 nm (Comparative Example 17), 1200 nm (Comparative Example 18), 2000 nm (Comparative Example 19), and 3100 nm (Comparative Example 20). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated.

The results are indicated in Table 1. The WF of electron transport layer 5 was 4.6 eV.

Comparative Examples 21 and 22

A glass substrate on which an ITO thin film (negative electrode) was formed was prepared, and the surface of this glass substrate was subjected to an oxygen plasma treatment (150 W for 15 minutes), then a solution obtained by diluting polyethyleneimine ethoxylate (PEIE) (available from Aldrich, trade name polyethylene, 80% ethoxylated solution, weight average molecular weight 110000) 100 times with water was used to obtain an electron transport layer 6 having a thickness of 10 nm and containing PEIE. A light detecting element was produced and EQE was measured in the same manner as in Example 1 described above except that the obtained electron transport layer 6 was used, and the thickness of the active layer was set to 600 nm (Comparative Example 21) and 1500 nm (Comparative Example 22). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 1. The WF of electron transport layer 6 was 4.7 eV.

Examples 6 and 7

A photoelectric conversion element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70IPH (available from Solenne, trade name: [C70]IPH, LUMO level: −4.3 eV) was used as the n-type semiconductor material contained in the active layer, the electron transport layer 1 described above was used as the electron transport layer, and the thickness of the active layer was set to 850 nm (Example 6) and 1100 nm (Example 7). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Example 23

A photoelectric conversion element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70IPH (available from Solenne, trade name: [C70]IPH, LUMO level: −4.3 eV) was used as the n-type semiconductor material contained in the active layer, the electron transport layer 1 described above was used as the electron transport layer, and the thickness of the active layer was set to 500 nm. The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Example 8

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70IPH was used as the n-type semiconductor material contained in the active layer, the electron transport layer 2 described above was used as the electron transport layer, and the thickness of the active layer was set to 1200 nm. The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 24 and 25

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70IPH was used as the n-type semiconductor material contained in the active layer, the electron transport layer 2 described above was used as the electron transport layer, and the thickness of the active layer was set to 250 nm (Comparative Example 24) and 750 nm (Comparative Example 25). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 26 and 27

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70IPH was used as the n-type semiconductor material contained in the active layer, the electron transport layer 3 was used as the electron transport layer, and the thickness of the active layer was set to 800 nm (Comparative Example 26) and 1400 nm (Comparative Example 27). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 28 and 29

A photoelectric conversion element was produced and EQE was measured in the same manner as in Example 1 described above except that C70IPH was used as used as an n-type semiconductor material contained in the active layer, an electron transport layer 7 having a thickness of 30 nm and containing zinc oxide was formed by using a zinc oxide dispersion liquid (available from Infinity PV, trade name Doped ZnO ink (water)), and the thickness of the active layer was set to 1000 nm (Comparative Example 28) and 1500 nm (Comparative Example 29). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2. In addition, the WF of electron transport layer 7 was 4.6 eV.

Example 9

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 except that C70PCBM (available from American Dye Source, trade name: ADS71BFA, LUMO level: −4.3 eV) was used as the n-type semiconductor material contained in the active layer, the electron transport layer 1 described above was used as the electron transport layer, and the thickness of the active layer was set to 1300 nm. The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 30 and 31

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 except that C70PCBM (available from American Dye Source, trade name: ADS71BFA, LUMO level: −4.3 eV) was used as the n-type semiconductor material contained in the active layer, the electron transport layer 1 described above was used as the electron transport layer, and the thickness of the active layer was set to 300 nm (Comparative Example 30) and 750 nm (Comparative Example 31). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Examples 10 and 11

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70PCBM was used as the n-type semiconductor material contained in the active layer, the electron transport layer 2 described above was used as the electron transport layer, and the thickness of the active layer was set to 1500 nm (Example 10) and 2000 nm (Example 11). The full width at half maximum (FWHM) of the peak on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 32 and 33

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70PCBM was used as the n-type semiconductor material contained in the active layer, the electron transport layer 2 described above was used as the electron transport layer, and the thickness of the active layer was set to 250 nm (Comparative Example 32) and 650 nm (Comparative Example 33). The full width at half maximum (FWHM) of the peak on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 34 to 36

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 except that C70PCBM was used as the n-type semiconductor contained in the active layer, the electron transport layer 3 described above was used as the electron transport layer, and the thickness of the active layer was set to 300 nm (Comparative Example 34), 800 nm (Comparative Example 35), and 1600 nm (Comparative Example 36). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Comparative Examples 37 to 39

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 described above except that C70PCBM was used as the n-type semiconductor contained in the active layer, the electron transport layer 7 described above was used as the electron transport layer, and the thickness of the active layer was set to 300 nm (Comparative Example 37), 900 nm (Comparative Example 38), and 1600 nm (Comparative Example 39). The full width at half maximum (FWHM) of the peak located on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 2.

Examples 12 to 14

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 except that a weight mixing ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material contained in the active layer was set to p/n=4/1 (Example 12), 10/1 (Example 13), 30/1 (Example 14), and the thickness of the active layer was set to 1500 nm. The full width at half maximum (FWHM) of the peak on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 3.

Comparative Example 40

A light detecting element was prepared and measurement values of EQE were obtained in the same manner as in Example 1 except that a weight mixing ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material contained in the active layer was set to 100/1 and the thickness of the active layer was set to 1500 nm The full width at half maximum (FWHM) of the peak on the longest wavelength side of the peaks of the EQE spectrum was calculated. The results are indicated in Table 3.

TABLE 1 Difference between work n-type Electron Work function Thickness semiconductor LUMO transport function and LUMO of active FWHM material (eV) layer (eV) (eV) layer (nm) (nm) Comparative C60PCBM 4.3 Electron 4.2 −0.1 550 600 Example 1 transport Example 1 layer 1 800 60 Example 2 1000 60 Example 3 1200 60 Comparative Electron 4.2 −0.1 650 600 Example 2 transport Comparative layer 2 750 600 Example 3 Example 4 1100 60 Example 5 1400 60 Comparative Electron 4.4 0.1 600 600 Example 4 transport Comparative layer 3 800 600 Example 5 Comparative 850 600 Example 6 Comparative 950 600 Example 7 Comparative 1100 600 Example 8 Comparative 1400 600 Example 9 Comparative 1800 600 Example 10 Comparative 3000 600 Example 11 Comparative 3500 600 Example 12 Comparative Electron 4.7 0.4 550 600 Example 13 transport Comparative layer 4 1000 600 Example 14 Comparative 1300 600 Example 15 Comparative 3200 600 Example 16 Comparative Electron 4.6 0.3 1000 600 Example 17 transport Comparative layer 5 1200 600 Example 18 Comparative 2000 600 Example 19 Comparative 3100 600 Example 20 Comparative Electron 4.7 0.4 600 600 Example 21 transport Comparative layer 6 1500 600 Example 22

TABLE 2 Difference between work n-type Electron Work function Thickness semiconductor LUMO transport function and LUMO of active FWHM material (eV) layer (eV) (eV) layer (nm) (nm) Comparative C70IPH 4.3 Electron 4.2 −0.1 500 600 Example 23 transport Example 6 layer 1 850 60 Example 7 1100 60 Comparative Electron 4.2 −0.1 250 600 Example 24 transport Comparative layer 2 750 600 Example 25 Example 8 1200 60 Comparative Electron 4.4 0.1 800 600 Example 26 transport Comparative layer 3 1400 600 Example 27 Comparative Electron 4.4 0.1 1000 600 Example 28 transport Comparative layer 7 1500 600 Example 29 Comparative C70PCBM 4.3 Electron 4.2 − 0.1 300 600 Example 30 transport Comparative layer 1 750 600 Example 31 Example 9 1300 60 Comparative Electron 4.2 − 0.1 250 600 Example 32 Transport Comparative layer 2 650 600 Example 33 Example 10 1500 60 Example 11 2000 60 Comparative Electron 4.4 0.1 300 600 Example 34 transport Comparative layer 3 800 600 Example 35 Comparative 1600 600 Example 36 Comparative Electron 4.6 0.3 300 600 Example 37 transport Comparative layer 7 900 600 Example 38 Comparative 1600 600 Example 39

TABLE 3 Difference between work n-type Work function semi- Electron func- and conductor LUMO transport tion LUMO p/n FWHM material (eV) layer (eV) (eV) ratio (nm) Example C60PCBM 4.3 Electron 4.2 −0.1 4/1 100 12 transport Example layer 2 10/1 100 13 Example 30/1 100 14 Compar- 100/1 ND ative Example 40

In Table 3, ND means that no peak was detected.

Hereinafter, the effects of the light detecting element according to the present embodiment will be described with reference to the drawings with reference to a part of examples and comparative examples.

FIGS. 4, 5, 6, and 7 illustrate the EQE spectrum (relative value) of the light detecting element according to Example 3, Comparative Example 8, Comparative Example 21 and Example 7, respectively, and the absorption spectrum (relative value) of the active layer according to Example 3, Comparative Example 8, Comparative Example 21, and Example 7, respectively.

As is clear from FIGS. 4 and 7, in Examples 3 and 7, in a region of wavelength 400 nm or more, the absorption peak located on the longest wavelength side is located near 810 nm, whereas among the peaks of the EQE spectrum, the peak located on the longest wavelength side is located near the wavelength of 870 nm, and is located in the near infrared wavelength region on the longer wavelength side.

On the other hand, the peak of the EQE spectrum did not appear near the wavelength of 810 nm where the absorption peak exists, and the sensitivity of EQE, that is, the light detecting element was lowered in this wavelength region. As a result, in Examples 3 and 7, the full width at half maximum (FWHM) of the peak of the EQE spectrum is a narrow peak of 60 nm in the near infrared wavelength region, and the light detecting element according to the example has a specific high sensitivity particularly in a narrow wavelength region in the near infrared wavelength region.

On the other hand, as illustrated in FIGS. 5 and 6, the light detecting element according to the comparative examples, in which the relationship between the thickness of the active layer, the work function, and the LUMO energy level of the n-type semiconductor material does not meet the requirements as described above, had a broad sensitivity over a fairly wide range including the visible light wavelength region.

FIG. 8 illustrates the EQE spectrum (relative value) of the light detecting element according to Example 10 and the absorption spectrum (relative value) of the active layer. As is clear from FIG. 8, if C70PCBM is used as the n-type semiconductor material in the active layer, the EQE in the visible light wavelength region can be suppressed to a low level. As a result, a narrow peak of the EQE spectrum with a full width at half maximum (FWHM) of 60 nm can be obtained only in the near infrared wavelength region. That is, if C70PCBM is used, it is possible to obtain a light detecting element having specifically high sensitivity only in a narrow wavelength region in the near infrared wavelength region.

FIGS. 9, 10, and 11 illustrate the EQE spectrum (relative value) of the light detecting element according to Example 12, Example 13, and Example 14 respectively, and the absorption spectrum (relative value) of the active layer according to Example 12, Example 13, and Example 14, respectively.

As is clear from FIGS. 9, 10, and 11, in Examples 3 and 7, in a region of wavelength 400 nm or more, the absorption peak located on the longest wavelength side is located near 800 nm, whereas among the peaks of the EQE spectrum, the peak located on the longest wavelength side is located near the wavelength of 910 nm, and is located in the near infrared wavelength region on the longer wavelength side.

On the other hand, the peak of the EQE spectrum did not appear near the wavelength of 800 nm where the absorption peak exists, and the sensitivity of EQE, that is, the light detecting element was lowered in this wavelength region. As a result, in Examples 12, 13, and 14, the full width at half maximum (FWHM) of the peak of the EQE spectrum is a narrow peak of 100 nm in the near infrared wavelength region, and the light detecting element according to the example has a specific high sensitivity particularly in a narrow wavelength region in the near infrared wavelength region.

As described above, by appropriately selecting and using various p-type semiconductor materials and n-type semiconductor materials particularly in consideration of the absorption wavelength thereof, the light detecting element having high sensitivity in a desired wavelength region (only) can be realized.

FIG. 12 illustrates the EQE spectrum (absolute value) of Examples 12 to 14 and Comparative Example 40. As is clear from FIG. 12, it is understood that there is a suitable ratio in the weight mixing ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material in the active layer. That is, from Examples 12 to 14, it is understood that the p/n ratio may be at least 4/1 to 30/1. On the other hand, it is understood that when the p/n ratio is 100/1, which is more than 1/99, it does not function as a light detecting element and thus it is not possible to obtain the specific sensitivity characteristics in a predetermined wavelength region.

DESCRIPTION OF REFERENCE SIGNS

-   1 Image detector -   2 Display device -   10 Light detecting element -   11, 210 Support substrate -   12 Negative electrode -   13 Electron transport layer -   14 Active layer -   15 Hole transport layer -   16 Positive electrode -   17, 240 Sealing substrate -   20 CMOS transistor substrate -   30 Interlayer insulating film -   32 Interlayer wiring portion -   40 Sealing layer -   50 Color filter -   100 Fingerprint detector -   200 Display panel unit -   200 a Display region -   220 Organic EL element -   230 Touch sensor panel 

1. A light detecting element comprising: a positive electrode; a negative electrode; and an active layer provided between the positive electrode and the negative electrode and containing a p-type semiconductor material and an n-type semiconductor material, wherein a thickness of the active layer is at least 800 nm, a weight ratio (p/n ratio) of the p-type semiconductor material to the n-type semiconductor material contained in the active layer is at most 99/1, and a work function of a surface in contact with the active layer on the negative electrode side is lower than an absolute value of a LUMO energy level of the n-type semiconductor material.
 2. The light detecting element according to claim 1, wherein external quantum efficiency has a narrow peak in a near infrared wavelength region.
 3. The light detecting element according to claim 2, wherein a full width at half maximum of the narrow peak is at most less than 300 nm.
 4. The light detecting element according to claim 1, wherein the surface is a surface of an electron transport layer provided between the negative electrode and the active layer.
 5. The light detecting element according to claim 1, wherein the n-type semiconductor material is a fullerene derivative.
 6. The light detecting element according to claim 5, wherein the fullerene derivative is C70PCBM.
 7. The light detecting element according to claim 2, wherein in a visible light wavelength region, the external quantum efficiency at the maximum absorption wavelength of the active layer is at most 20% of the maximum value of the external quantum efficiency of the narrow peak.
 8. An image sensor including the light detecting element according to claim
 1. 9. The light detecting element according to claim 2, wherein the surface is a surface of an electron transport layer provided between the negative electrode and the active layer.
 10. The light detecting element according to claim 3, wherein the surface is a surface of an electron transport layer provided between the negative electrode and the active layer.
 11. The light detecting element according to claim 2, wherein the n-type semiconductor material is a fullerene derivative.
 12. The light detecting element according to claim 3, wherein the n-type semiconductor material is a fullerene derivative.
 13. The light detecting element according to claim 4, wherein the n-type semiconductor material is a fullerene derivative.
 14. The light detecting element according to claim 3, wherein in a visible light wavelength region, the external quantum efficiency at the maximum absorption wavelength of the active layer is at most 20% of the maximum value of the external quantum efficiency of the narrow peak.
 15. The light detecting element according to claim 4, wherein in a visible light wavelength region, the external quantum efficiency at the maximum absorption wavelength of the active layer is at most 20% of the maximum value of the external quantum efficiency of the narrow peak.
 16. The light detecting element according to claim 5, wherein in a visible light wavelength region, the external quantum efficiency at the maximum absorption wavelength of the active layer is at most 20% of the maximum value of the external quantum efficiency of the narrow peak.
 17. The light detecting element according to claim 6, wherein in a visible light wavelength region, the external quantum efficiency at the maximum absorption wavelength of the active layer is at most 20% of the maximum value of the external quantum efficiency of the narrow peak.
 18. An image sensor including the light detecting element according to claim
 2. 19. An image sensor including the light detecting element according to claim
 3. 20. An image sensor including the light detecting element according to claim
 4. 